Nondependent Lung Ventilation and Fluid Responsiveness

The stroke volume variation (SVV), measured using the Vigileo-FloTrac system (Edwards Lifescience, Irvine, CA), has been shown to able to predict fluid responsiveness during one-lung ventilation (OLV) in patients undergoing pulmonary lobectomy (sensitivity: 82.4%, specificity: 92.3%).1 Many parameters such as tidal volume (TV),1-2 positive end-expiratory pressure (PEEP),3 respiratory rate (RR), 4 chest and lung compliance,5 heart rate and rhythm, and ventricular function and afterload,6-7 all have been documented to have effects on the SVV. SVV is calculated as the variation of beat-to-beat SV from the mean value during the most recent 20 seconds of data: SVV = (SVmax - SVmin)/SVmean, where SVmax, SVmin, and SVmean are, respectively, the maximum, minimum, and mean SV determined by the system. SVV may not be sufficiently sensitive to predict fluid responsiveness in patients with right ventricular (RV) dysfunction due to concomitant increases in RV afterload, that lead to a decrease in preload variation and subsequent inaccuracy in SVV measurements.8 OLV may increase airway pressure, resulting in increases in the RV afterload, end-diastolic volume, and stroke work index, thus impeding RV function.9-11The increases in the right ventricular afterload may exaggerate the cyclic variation in stroke volume.12 In the authors' previous study,9 they found that the high-frequency positive-pressure ventilation (HFPPV) was superior to continuous positive-airway pressure (CPAP) for OLV, resulting in significantly higher RV ejection fraction, lower RV afterload and higher arterial oxygenation, whereas the former limiting the adequate operative field visualization during video-assisted thoracoscopic surgery (VATS).13 The effects of the nondependent lung ventilation with HFPPV and CPAP on the SVV and fluid responsiveness during OLV has not yet been studied.